1. Field of the Invention
This invention relates to a device for moving an optical head including lenses and so on, and, more particularly, to such a device wherein a light irradiating position at which a light beam is focused by an optical head may not be readily affected by error in movement of the optical head.
2. Description of the Prior Art
As a typical method of recording a continuous signal on a recording medium over a long period of time, there has been adopted such, method that tracks in a spiral form are incised on a disk-shaped recording medium, and a "record" which is a disk-shaped recording medium with sound signals recorded thereon has such signal tracks as described above.
In the recording method referred to above, the radial pitch of the signal tracks on the disk-shaped recording medium is determined by the amount of feed of the record head per revolution of a turn table in a record prototype forming apparatus on which the recording medium is placed.
In the production of the prototype of a record, the pitch of the tracks may be considerably great because the recorded signals are not of so high frequency, and therefore the use of the conventional feed screws and the rotating mechanism therefor has resulted in no objectionable pitch irregularity. However, in the "video disk" which has progressively been developed in these years, it is desired that television signals containing over one hundred times as those as many informations contained in the sound record be recorded on a recording medium of a size similar to that of the conventional record, so that, during the production of a video disk prototype, it is necessary to optically record the signals to thereby provide finer signal tracks. It is also imperative to greatly limit the radial pitch of the spirally recorded signal tracks in order to record as many informations as possible. For example, when TV signals of a length of 30 minutes or so are to be recorded on a disk of a size corresponding to that of a 30 cm LP record, the radial pitch of the signal tracks formed in spiral must be selected to a value of several microns.
Thus, in the production of a video disk prototype, the feed of signal light onto the record prototype must be effected with high accuracy.